Recently, several lines of investigation have led to the conclusion that many of the significant alterations of cell behavior upon transformation, such as loss of growth control, are related to the altered translational mobility of certain surface components. There is evidence that contractile proteins influence translational mobility of surface components and thus play a role in the maintenance of cell surface expressions and in the growth control of normal and transformed cells. The research outlined in this proposal is aimed at eludicating the regulation of the assembly of contractile proteins and the molecular structure of the linkage of these proteins with membranes. A comparative study of normal and viral transformed cells is proposed to pinpoint significant structural changes during cell transformation. The first part of the proposal in an investigation of the molecular arrangement of membrane-associated contractile proteins of normal and transformed culture cells, and of human erythrocytes. Specific antibodies will be used to identify and localize contractile proteins in isolated plasma membranes. The chemical crosslinking technique will be used to study the degree of polymerization and the neighbor relationship of these proteins, and to search evidence for trans-membrane linkages. The second part is an investigation of the control mechanisms of cytoplasmic contractile apparatus. The protein filamin is used as a specific probe for the assembly properties of actin containing filaments in normal and transformed cells. The interaction of filamin with actin will be studied by physical methods, and the cellular distribution of filamin and other contractile proteins will be examined by fluorescent antibody labelling techniques.